Effect of chemical cleaning and membrane aging on membrane biofouling using model organisms with increasing complexity

A major obstacle in the widespread application of membrane microfiltration for activated sludge wastewater treatment is the rapid decline of the permeation flux with time as a result of membrane fouling. Nowadays, fouling is mostly controlled by optimal operational conditions, and physical and chemical cleaning. In this study, the efficiency of chemical cleaning and the impact of these chemicals on the membrane structure (membrane aging) has been evaluated and linked to properties of the microbial community present in the feed. Three polymeric microfiltration membranes (polyvinyldifluoride, polyethylene and polysulfone) and 3 model biofoulants with increasing complexity were used in a cross-flow filtration set-up. The cleaning efficiency was measured in terms of bacterial cell density and exopolymeric substance concentration. Membrane cleaning by 1% NaOCl and 2% citric acid had a cleaning efficiency ranging from 57 to 100% and 41 to 100% respectively, depending on the concentration and the complexity of the used biofoulants. Membrane aging by NaOCl and citric acid was reflected in an increased membrane pore size and surface porosity, while the membrane hydrophobicty and surface chemistry of the membrane surface remained unaffected. Differences in bacterial cell densities were found on aged membrane, but the results were strongly biofoulant dependent. On the other hand, significantly higher exopolymeric substances concentrations were detected on the aged membranes, suggesting that the biofoulants behave differently on aged membranes. (C) 2014 Elsevier B.V. All rights reserved.